A nonvolatile semiconductor memory device using a semiconductor element such as an EEPROM, an AND-type flash memory, a NOR-type flash memory, and a NAND-type flash memory is widely known. Among them, the NAND-type flash memory has an advantage in high density because each of memory cells shares a source-drain diffusion layer.
A word line switch unit is provided at an edge portion of a memory cell array of the NAND-type flash memory, in which a word line switch transistor that transfers a voltage to a word line of the memory cells is formed. To reduce the area of the word line switch unit, it is desired to reduce a write voltage (program voltage) during a data write operation, and to downsize a transistor.